The subjects of this investigation are two prokaryotic organisms, Thermoplasma acidophilum and Sulfolobus acidocaldarius, each of of which has a protein closely resembling eukaryotic histones that is associated with its DNA. The long range goals of these studies are (1) to understand the functions of these proteins, and (2) to assess the possible evolutionary relationship of these organisms to eukaryotic cells. One project is to determine the complete amino acid sequence of the T. acidophilum protein, which we are doing in collaboration with Robert DeLange of U.C.L.A. This information should reveal the relationship of this protein to eukaryotic histones. Another project will be to complete the isolation and characterization of the S. acidocaldarius nucleoprotein and histone-like protein, a project that is currently in its initial stages. These are partially interesting organisms because both lack rigid cell walls. For Sulfolobus, at least, this is clearly related to its mode of nutrition; it is a chemo-autotroph that can obtain energy by oxidizing elemental sulfur to sulfuric acid. The cells can wrap around and adhere to sulfur crystals, thus resembling a primitive form of phagocytosis. In addition, we have found evidence for the contractile proteins actin and myosin in these cells (and also in T. acidophilum), and are currently attempting to purify them for unambiguous identification. BIBLIOGRAPHIC REFERENCES: Searcy, D.G., 1976, Thermoplasma acidophilum: intracellular pH and potassium concentration. Biochim. Biophys. Acta 451: 278-286. Searcy, D.G., 1976, Thermoplasma acidophilum: studies on a prokaryote that contains a histone-like protein. In Molecular Mechanisms in the Control of Gene Expression, Academic Press, New York.